I have been playing Book of Heroes casually for a couple months now. It's fun, and modestly social if you are raiding in guilds.
But the clincher? The rats. Oh, man. Check this guy out. He's a rat, riding a bigger rat, swinging a flail made from the skull of a rat. Way to pack in the rats, Book of Heroes. The rat people are called Rath'een, and are the closest thing to Skaven I think they could include without needing to retain legal counsel. I was amused that the proper names for the Rath'een could have come right out of The Underempire too. Skar? Trask? Yeah, pretty sure I remember them. Heck, maybe the authors hung out there and the names are an homage. If I run into a Vorg I'll know it's true.